[CHEM] question

[299678]

Advertisement - Members don't see this ad

Which of these changes will produce the most positibe voltage for this half reaction in the direction written?

CO^2+ + 2e- ------> CO (s) E potential = -0.28 v
a) increasing the amount of solid CO
b) decreasing the amount of solid CO
c) increasing the concentration of CO^2+
d) decreasign the concentration of CO^2+

Sorry I have no answer for this question. Need ur reasoning to support your answer.

I have reasoning for this, but don't know how to input variables.
Nernest equation

E = E standard - (0.0592/n)Log Q

Q = Product / reactant

Q = A/B when B increase, E increase
When A increase, E decrease


2. Which compound is not expected to be colored?
A. CuCl2
B. K2Cr2O7
C. TiO2
D. NiSO4

I had very similar question like this on organic section on real DAT. Anyone can explain this?
answer is c

 

[amcmahon]

So the answer to the first question is C. The reason is because solid compounds have no effect on the Ksp. We need to keep in mind the 3 rules for when a solution is at equilibrium. 1. Ksp = 0. 2. (delta)G=0. and 3. Ecell=0. If we add CO(aq) to the solution then we will have more reactants and the equilibrium will shift to the right.

For question 2, its hard to know but Cu tends to produce a blue substance. Cr tends to be red. From there I would have guessed between Ni and Ti. I just looked some info up on wikipedia and it looks like there are only 6 compounds are colored.

Co(NO3)2 (red);
K2Cr2O7 (orange);
K2CrO4 (yellow);
NiCl2 (green);
CuSO4 (blue);
KMnO4 (violet).

http://en.wikipedia.org/wiki/File:Coloured-transition-metal-solutions.jpg

 

[TriCuspid]

Has to do with the d-orbitals for the coloring. Ti is in the p-orbitals.

 

[txlonghorn]

It is asking which will produce the most voltage, so is it not asking when voltage will be positive? As written, it requires voltage.

 

[299678]

CO^2+ + 2e- ------> CO (s) E potential = -0.28 v
It is negative voltage, so non spontaneous so when we reverse the reaction

CO(s) ------------> Co^2+ + 2e- = (+) 0.28 so Le chandler principle,
when we decrease CO^2, we get more product, so increasing voltage? so I guess answer is d) ??

what do you guys think?

Also how do you know Ti is in p orbital?